There is known an air intake rate control device for electrically controlling the opening and closing operation of a control valve placed in a bypass passageway bypassing an intake throttle valve by means of idle speed control (ISC) and controlling the air intake rate to the engine by regulating the bypass air rate passing through the bypass passageway, thereby to control the engine speed when the engine is idling.
The idle speed control (ISC), as shown in FIG. 6, drives the control valve to obtain a target engine speed corresponding to the cooling water temperature of the engine, and feedback controls the engine speed.
As is shown in FIG. 7, this feedback control determines whether both a first condition requiring an idle switch to be in its active (ON) state and a second condition requiring the engine speed to be lower than a target engine speed are satisfied. If the idle switch has been in its active state for a delay time, or if both of the aforementioned first and second conditions are satisfied, and if a further condition requiring the vehicle speed to be lower than a comparable vehicle speed at the start of control, and a still further condition requiring the engine speed to be lower than a comparable engine speed at the start of control as shown in FIG. 8 are also satisfied, then the feedback control is started.
In case the conditions required for starting the feedback control are not satisfied, an ISC duty rate of the control valve is maintained fixed and a fixed control is performed.
Furthermore, when in deceleration, the deceleration control system as a dash pot portion is actuated upon actuation of the idle switch and the air intaking rate is increased to prevent a decrease of engine speed and engine stall (see FIGS. 9(a) and 9(b)).
As is shown in FIG. 10, actuation of the prior art deceleration control system is triggered if both a first condition requiring the engine speed to be equal to or lower than a fuel cut engine speed and a second condition requiring the idle switch to be in its active (ON) state are satisfied, or if a third condition wherein the driving state has recovered from fuel cut is satisfied.
Also, as shown in FIG. 11, for triggering the start of the fuel cut control of FIGS. 9a and 9b is to satisfy either a first condition wherein the engine speed is 4000 rpm or more and the idle switch is in its active (ON) state, or a second condition wherein the engine speed is equal to or more than the fuel cut engine speed but less than 4000 rpm and the idle switch is in its active (ON) state.
One example of a conventional air intake rate control device is disclosed in Japanese Patent Early Laid-open Publication No. Sho 63-68738. The air intake rate control device disclosed in this Publication is constructed such that in an intake rate control device for feeding air into an intake passageway on the downstream side of a throttle valve when the engine is being decelerated, a reducing rate per unit time of the deceleration air is varied by control means in accordance with the driving state of the engine. For example, when the engine speed is high in an early stage of deceleration, the reducing rate is increased to provide a decelerating feeling and the reducing rate is decreased in accordance with the lowering of the engine speed as it comes close to a later stage of deceleration, in order to prevent deceleration shock.
Japanese Patent Early Laid-open Publication No. Sho 63-208638 discloses another known control device which comprises bypass air control means for feeding a predetermined quantity of bypass air which is to be gradually reduced when the engine is decelerating, fuel cut means for cutting fuel at deceleration, and air rate detection means for detecting the bypass air flow rate. The air rate detection means is set such that the fuel cut operation is performed for deceleration when the bypass air flow rate becomes less than a predetermined quantity, thereby to prevent generation of hatching and to improve driving performance.
In the conventional intake rate control device, the deceleration control system is actuated every time the fuel cut operation is performed. Therefore, when the temperature of the engine cooling water is low, the engine speed is increased by the air rate resulting from actuation of the deceleration control system and by the air rate coming from an air regulator, thus generating an awkward feeling of physical disorder and deteriorating the driving performance. Also, when the changing operation of a shift lever is effected and ON/OFF operation of an accelerator switch for detecting the amount of depression of the accelerator is effected, the deceleration control system is actuated to increase the intake rate more than necessary as shown by the hatched area of FIG. 12, thus again generating an awkward feeling of physical disorder while driving and deteriorating the driving performance.
Furthermore, when the idle switch is brought to its inactive (OFF) state from its active (ON) state, the deceleration control system is actuated, and when a hard braking is effected or the clutch discs are disconnected after the passage of a short time from when the accelerator switch is turned OFF, the deceleration control system is not actuated and the engine speed is lowered, and finally engine stall results.
Therefore, the object of the present invention is, for the purpose of obviating the above inconveniences, to provide an air intake rate control device of an internal combustion engine which includes control means for actuating said deceleration control system only when it satisfies the conditions that the cooling water temperature of the engine is equal to a preset water temperature or higher, than an accelerator switch is in its inactive state and therefore the engine is decelerating, that said engine speed is equal to or lower than the actuation speed of said deceleration control system, and that the reductive change rate of engine speed is equal to or larger than an actuation differential change rate of said deceleration control system, the control means deciding a duty rate of said deceleration control system in such a manner as to be in correspondence with the reductive change rate of the engine speed, and increasing the air intake rate, whereby unnecessary actuation of the deceleration control system is prevented, driving performance is enhanced, the duty rate of the deceleration control system can be decided in such a manner as to be in correspondence with a reductive change rate of engine speed, and decreases in engine speed and subsequent engine stall can be prevented by properly increasing the air intaking rate.
In order to achieve the above, according to the present invention, in an air intaking rate control device of an internal combustion engine for controlling an air intaking rate in such a manner as to control the engine speed so that it corresponds to the temperature of cooling water of the engine and to actuate a deceleration control system for feeding bypass air into said internal combustion engine bypassing an intake throttle valve upon actuation of an idle switch at deceleration, said air intaking rate control device includes control means for actuating said deceleration control system only when it satisfies the conditions that (1) said temperature of cooling water of said engine is equal to or higher than a preset water temperature, (2) an accelerator switch is in its inactive state and the engine is decelerating, (3) said engine speed is equal to or lower than the actuation speed of said deceleration control system, and (4) said reductive change rate of engine speed per unit time is equal to or larger than an actuation differential change rate of said deceleration control system. A duty rate of a control signal applied to said deceleration control system is decided in such a manner as to be in correspondence with a reductive change rate of engine speed. The air intaking rate is controlled to be increased by the control means, unnecessary actuation of the deceleration control system is prevented, driving performance is enhanced, and lowering of the engine speed and subsequent engine stall are prevented by properly increasing the air intaking rate.